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package org.openjdk.jmh.samples;


import org.openjdk.jmh.annotations.*;

import org.openjdk.jmh.infra.Blackhole;

import org.openjdk.jmh.runner.Runner;

import org.openjdk.jmh.runner.RunnerException;

import org.openjdk.jmh.runner.options.Options;

import org.openjdk.jmh.runner.options.OptionsBuilder;


import java.util.concurrent.TimeUnit;


@BenchmarkMode(Mode.AverageTime)

@OutputTimeUnit(TimeUnit.NANOSECONDS)

@State(Scope.Thread)

public class JMHSample_09_Blackholes {


 /*

  * Should your benchmark require returning multiple results, you have to

  * consider two options (detailed below).

  *

  * NOTE: If you are only producing a single result, it is more readable to

  * use the implicit return, as in JMHSample_08_DeadCode. Do not make your benchmark

  * code less readable with explicit Blackholes!

  */


 double x1 = Math.PI;

 double x2 = Math.PI * 2;


 /*

  * Baseline measurement: how much single Math.log costs.

  */


 @Benchmark

 public double baseline() {

  return Math.log(x1);

 }


 /*

  * While the Math.log(x2) computation is intact, Math.log(x1)

  * is redundant and optimized out.

  */


 @Benchmark

 public double measureWrong() {

  Math.log(x1);

  return Math.log(x2);

 }


 /*

  * This demonstrates Option A:

  *

  * Merge multiple results into one and return it.

  * This is OK when is computation is relatively heavyweight, and merging

  * the results does not offset the results much.

  */


 @Benchmark

 public double measureRight_1() {

  return Math.log(x1) + Math.log(x2);

 }


 /*

  * This demonstrates Option B:

  *

  * Use explicit Blackhole objects, and sink the values there.

  * (Background: Blackhole is just another @State object, bundled with JMH).

  */


 @Benchmark

 public void measureRight_2(Blackhole bh) {

  bh.consume(Math.log(x1));

  bh.consume(Math.log(x2));

 }


 /*

  * ============================== HOW TO RUN THIS TEST: ====================================

  *

  * You will see measureWrong() running on-par with baseline().

  * Both measureRight() are measuring twice the baseline, so the logs are intact.

  *

  * You can run this test:

  *

  * a) Via the command line:

  *    $ mvn clean install

  *    $ java -jar target/benchmarks.jar JMHSample_09 -f 1

  *    (we requested single fork; there are also other options, see -h)

  *

  * b) Via the Java API:

  *    (see the JMH homepage for possible caveats when running from IDE:

  *      http://openjdk.java.net/projects/code-tools/jmh/)

  */


 public static void main(String[] args) throws RunnerException {

  Options opt = new OptionsBuilder()

          .include(JMHSample_09_Blackholes.class.getSimpleName())

          .forks(1)

          .build();


  new Runner(opt).run();

 }

// 本例是为了解决（8）中死码消除问题，JMH提供了一个 Blackholes （黑洞），这样写就不会被编译器消除了。

}